The present invention relates generally to steering systems for automotive vehicles, and more particularly, to a misalignment detection system for the steering system.
Automotive vehicles depend on aligned wheels for smooth travel and predictable steering efforts, as well as even wear of tires and related suspension parts. During operation of an automotive vehicle, the steering system may become misaligned. Several patents relating to road wheel alignment and alignment adjustment include U.S. Pat. No. 5,988,311 Electric Steering Actuator; U.S. Pat. No. 5,941,338 Vehicle Steering Correction System; U.S. Pat. No. 5,026,081 Rear Wheel Steering System Having Toe Error Compensation; U.S. Pat. No. 4,835,714 Wheel Alignment Control System For Vehicles; U.S. Pat. No. 3,597,728 Means of Instantly Detecting Anomalies On A Moving; U.S. Pat. No. 5,790,966 Method for Determining Steering Position of Automotive Steering Mechanism; and U.S. Pat. No. 5,787,375 Method for Determining Steering Position of Automotive Steering Mechanism. Vehicle Misalignment can occur in an automotive vehicle for various reasons. Driving over potholes, road debris, curbs or rough roads can cause the adjusting mechanisms or the actual vehicle structure itself to change, resulting in steering system misalignment.
A misalignment in the present application refers to a misalignment of the steered or road wheels with respect to their alignment specifications as provided by the vehicle manufacturer, specifically, caster, camber, toe-in and/or Ackerman Angle. Misalignment can manifest itself through increased steering efforts or, if allowed to continue, as increased tire and suspension bushing wear. Misalignment can also result in unpredictable and hazardous vibrations and steering efforts. Until the tires or bushings exhibit noticeable wear or the vehicle exhibits shudders at certain speeds, misalignment is often difficult to detect. Once the wear is noticeable on the tires or bushings or the vehicle shudders unpredictably, the damage is unfortunately already done.
It would therefore be desirable to provide a misalignment detection system for an automotive vehicle that signals the driver to the presence of misalignment so that corrective actions may be taken.
The present invention provides a misalignment detection system for a steering system of an automotive vehicle, which includes a vehicle speed sensor, steering wheel torque sensor, a steering wheel angle sensor, a lateral acceleration sensor, a yaw rate sensor, and a memory/logic device. A vehicle speed sensor generates a vehicle speed signal indicative of the speed of the vehicle. A steering wheel torque sensor generates a wheel torque signal indicative of the torque applied to the steering wheel by the driver. A steering wheel angle sensor generates a steering wheel angle signal indicative of the angle induced into the steering wheel by the driver. A lateral acceleration sensor generates a lateral acceleration signal indicative of the lateral acceleration experienced by the vehicle. A yaw rate sensor generates a signal indicative of the yaw rate of the vehicle. A memory device stores previous sensor history and/or a steering angle value derived from alignment specifications provided by the automobile manufacturer. A logic device analyzes various sensor signals to determine whether misalignment exists or not. In its most basic form, the system uses the yaw rate and lateral acceleration sensors to determine whether the vehicle is being driven in a substantially straight line and if so, then looks at the signal from the steering wheel torque sensor to determine if the operator is having to adjust the wheel to maintain this straight line motion. If the driver input correction as detected by the steering wheel torque sensor value exceeds a predetermined level while the vehicle is traveling in a straight line, misalignment exists. The logic device can also be fashioned so as to apply simple logic functions to the various signal values to rule out other explanations for the error value, such as road bank and crown.
One feature of the present invention is that upon a predetermined amount of error, the vehicle operator may be presented with an indicator to inform him of the misalignment. In one aspect of the invention, a method for determining misalignment comprises the steps of:
detecting a vehicle speed;
determining an empirical steering wheel angle derived from yaw rate, vehicle speed and a steering ratio map;
determining if vehicle is driving in a substantially straight line;
if so, then sensing a steering wheel applied torque;
determining an error between the steering wheel applied torque signal and the stored steering wheel torque signal when driving substantially straight; and
indicating a misalignment condition if the error is above a predetermined level.
In another aspect of the present invention, various other vehicle condition sensors are used to check the error to insure it is accurate. Such vehicle condition sensors include (but are not limited to) a vehicle lateral acceleration sensor, a vehicle yaw rate sensor and a steering wheel angle sensor.
In another aspect of the present invention, the misalignment detection system can be used to adjust the alignment in electrically steered vehicles that have independent actuators to adjust the steered road wheels.
One advantage of the invention is that by signaling the vehicle operator of a misalignment, excessive wear of the vehicle""s tires and bushings can be reduced by corrective action. Another advantage of the invention is that diagnosis of misalignment no longer would rely on expensive machines and labor by a trained technician. This will result in reduced diagnosis costs to the vehicle owner. The misalignment detection system may store specific information from the various vehicle condition sensors in an on-board diagnostic system for downloading by a technician. This information may be able to help guide the technician to specific mechanical adjustments to be made to correct the misalignment, thus further reducing the costs of corrective action. Yet another advantage of the invention is that many of the sensors can be used by other systems of the vehicle. Therefore, implementation of a misalignment detection system may be done in a cost efficient manner.
Other objects, features and advantages of the invention will become apparent when viewed in the light of the detailed description of the preferred embodiment when taken in conjunction with the attached drawings and appended claims.